Radiocontrast agents (or simply contrast agents) are compounds used to improve the visibility of internal bodily structures in an X-ray image. In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

Contrast agents are also used in MRI (Magnetic Resonance Imaging). Although MRI is usually considered a branch of radiology, it is not based on X-rays. MRI contrast agents are usually Gadolinum-based, and work not by being radioopaque, but rather by altering the magnetic properties of nearby hydrogen nucleii. For other meanings see Magnetic Resonance Imaging (MRI). ...

Types and uses

There are two basic types of contrast agents used in X-ray examinations. In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

One type of contrast agent is based on barium sulphate, an insoluble white powder. This is mixed with water and some additional ingredients to make the contrast agent. As the barium sulphate doesn't dissolve, this type of contrast agent is an opaque white mixture. It is only used in the digestive tract; it is usually swallowed or administered as an enema. After the examination, it leaves the body with the faeces. Barium sulfate (or barium sulphate, BaSO4) is a compound (a type of salt made from barium and sulphur) frequently used clinically as a radiocontrast agent for X-ray imaging and other diagnostic procedures. ... Water (from the Old English word wæter; c. ... Barium sulfate (or barium sulphate, BaSO4) is a compound (a type of salt made from barium and sulphur) frequently used clinically as a radiocontrast agent for X-ray imaging and other diagnostic procedures. ... Rabbit feces are usually 0. ...

The other type of contrast agent is based on iodine. There are different molecules, such as iohexol, iodixanol, ioversol and many others. The basic idea is to chemically bind the iodine in an large organic molecule making it water soluble and as harmless as possible to the body. These contrast agents are sold as clear colorless water solutions, the concentration is usually expressed as mg I/ml. Modern iodinated contrast agents can be used almost anywhere in the body. Most often they are used intravenously, but for various purposes thay can also be used intraarterially, intrathecally and intraabdominally. General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Atomic mass 126. ... An intravenous drip in a hospital Intravenous therapy or IV therapy is the administration of liquid substances directly into a vein. ...

An older type of contrast agent, Thorotrast was based on thorium dioxide, but this was abandoned since it turned out to be carcinogenic. Thorotrast is a suspension containing particles of the radioactive compound thorium dioxide, ThO2, used as a contrast medium in X-ray diagnostics in the 1930s and 40s (use in some countries, such as the U.S. continued into the 1950s). ... Thorium dioxide (ThO2), also called thorium(IV) oxide (IUPAC) is a white, crystalline powder. ... In pathology, a carcinogen is any substance or agent that promotes cancer. ...

Side-effects

Modern iodinated contrast agents are safe drugs; adverse reactions exist but they are uncommon.

For patients with previously impaired renal function, however, large doses of iodinated contrast agents may cause contrast-induced nephropathy. The risk is augmented if the patient also has other predisposing conditions; notably diabetes mellitus, dehydration and myeloma. In medicine (nephrology) renal function is an indication of the state of the kidney and its role in physiology. ... Diabetes mellitus is a medical disorder characterized by varying or persistent hyperglycemia (elevated blood sugar levels), especially after eating. ... Multiple myeloma (also known simply as myeloma or plasma cell myeloma) is a hematological malignancy of plasma cells, the cells of the immune system that produce antibodies. ...

The osmolality of the contrast agent is believed to be of great importance in contrast-induced nephropathy. Ideally, the contrast agent should be isoosmolar to blood. Modern iodinated contrast agents are non-ionic, the older ionic types caused more adverse effects and are not used much anymore. Osmolality, in biology and chemistry, is a measure of moles of solute per kilogram of solvent. ... Red blood cells (erythrocytes) are present in the blood and help carry oxygen to the rest of the cells in the body Blood is a circulating tissue composed of fluid plasma and cells (red blood cells, white blood cells, platelets). ...

To minimize the risk for contrast-induced nephropathy, various actions can be taken if the patient has predisposing conditions. Low-osmolar or iso-osmolar contrast media slould be chosen. The dose of contrast media should be as low as possible, while still being able to perform the necessary examination. Dehydration should be corrected before the examination, this is usually done by means of intravenous fluids. An intravenous drip in a hospital Intravenous therapy or IV therapy is the administration of liquid substances directly into a vein. ...

Some recent studies suggest that N-acetylcysteine protects the kidney from the toxic effects of the contrast agent (Gleeson & Bulugahapitiya 2004). This effect is, in any case, not overwhelming. N-acetylcysteine is a chemical, commonly called NAC, produced by the body that enhances the production of the co-enzyme glutathione, a powerful antioxidant. ...

Other pharmacological agents, such as theophylline and furosemide have been tried, but they have not been shown to have beneficial effects against contrast-induced nephropathy. Theophylline is a methylxanthine drug and is used in therapy for respiratory diseases. ... Furosemide (INN) or frusemide (former BAN) is a loop diuretic used in the treatment of congestive heart failure and oedema. ...

References

• Gleeson TG, Bulugahapitiya S. Contrast-induced nephropathy. AJR Am J Roentgenol 2004;183:1673-89. PMID 15547209.